I've been lurking here for a few years, looking at the suggestions but never had a lot to say, but I just started a big project, which might be of interest (if only for being so strange).

I've just broken ground on construction of a new outbuilding. I'd like it to contain a home theatre, but it needs to be multipurpose, so some major compromises have to be made. The general plan is a triple garage on the main level, with a patio/roof garden above, and a basement below, all built from reinforced concrete. The basement will have a 23ft x 23ft main room, 11ft x 11ft side room, and a 11ft x 11ft stairwell that will also be a machinery space (under the stairs).

The primary purpose of the main room is to be a robotics laboratory. For this it needs to be clear with a smooth floor. To simplify things I've decided to make the walls/floor/ceiling all black marble with a glowing isogrid (2 foot spacing), to be achieved by using diffuser LED strips (RGB on dimmers) for the tile joins. It also needs good but optional power, networking and cooling. My plan is 3 phase 240V power supply (70KW) with isolation transformers, surge supression, filtering etc, eight 500mm axial fans feeding strips of ventilation grill, and water cooling via washing machine plumbing connectors, circulation pumps and radiators on the roof (also full copper foil faraday cage and all fireproof materials/doors). Any resemblence to Star Trek holodeck completely coincidental.

The secondary purpose is to be a home cinema which is a challenge to combine with above. I'm thinking an LG 98UB980V for the main display; to date I have always been a projector fan, but this needs to be usable as a computer display when the room lights are on. Onkyo TX-NR3030 should suffice for the 11.2 receiver? My current Onkyo has served me well for 9 years now, and 250W/channel seems like enough for a space this size. MINX MIN22 speakers for the side channels; should be 'good enough' without having to have acoustic transparent panels (can fire through the ventillation grills).

Haven't chosen main speakers yet, but they can go in the main niche with the TV. To each side will be niches with tinted glass doors for PCs, 2ft cube areas underneath for subwoofers. I might hang another couple of 4K TVs from the ceiling as secondary displays. Speaking of which, for seating I was thinking a few 'royal globo' hanging garden chairs (to keep the floor clear), maybe with some little LED lights added to the frame (powered from above).

The smaller room needs to work as a spare bedroom but I'd also like to get a bar in there. I think I can just about squeeze in a four-seater bar using a flip-up counter. Pocket doors all around for better space utilisation. The biggest problem will definitely be that a 23ft x 23ft x 8ft space with minimal furniture and floor/walls/ceiling all covered in marble tiles will be an absolute echo chamber. Probably need some minimalist absorbers for it to be usable, e.g. 1 foot square sections of black pyramid foam stuck in the centre of the tiles, or some hanging clear plastic globes.

Alas I would add plans/photos but I lurked for too long and don't have the post count.

I don't know about anyone else, but this certainly has my attention.

23' x 23' x 8' with hard reflective surfaces all around is probably going to sound horrible, BTW. Some heavy-duty acoustic treatment is going to be needed, but I think that's not going to be a problem for you.

The problem is really just that I need flat waterproof surfaces (and a hard polished floor) when not being used as a HT, otherwise I could tile all surfaces with black absorber panels instead of marble. I am planning to put in the full 11 x 11 grid of 500kg load rated ceiling eyes (at tile centres), so potentially I could just have lots of removable absorber panels that hang from the ceiling. Honeycomb translucent sound insulation maybe? Hopefully I can get away with a hard floor if there is good ceiling and wall coverage.

That might work. I've never done anything like that, so can't offer much advice. Hopefully one of the acoustics guys here can chime in.

Here's the plan and the site. The structural engineer wants to change most of the steel beams to concrete though.

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An update on this. The structural engineer moved the soakaway to elsewhere on the site, which frees up some space. I've been considering the cost of a good 4K flat panel, e.g. XBR-100Z9D, versus the cost of just digging and concreting the extra space for a rear-projection setup. The later looks favourable. So how about;

3m wide x 2m deep alcove in north wall to provide projection space. 3.2m x 1.8m screen with 4.5m optical path length, allowing 0.5m depth for the projector. VPL-VW1100ES projector (2000 lumen 4K). I'd need an optical quality mirror, careful setup of vertical angle on mirror and projector (since the max vertical offset is only 80%, can't use a flat mirror), and a good quality 153" rear projection screen. I think 2000 lumens rear projected onto 153" should give decent contrast even with some ambient light?

Thinking about all the cool 2.4:1 setups I've seen here, I'm seriously considering widening the screen to 4.2m x 1.8m (bezel dimensions). This would mean going to a dual mirror setup as I can't reasonably make the rear projection space longer than 2.5m. Would 2000 lumens still be enough to rear-project a screen of that size? I'm assuming Stewart Filmscreen 100 or equivalent with a nominal gain of 1.0; much as I'd like to go to a 1.5 gain material (e.g. Filmscreen 150), that would increase the centre to edge gain difference from less than 20% to more than 30%, even allowing for the lower incidence angle with the double mirror setup. The VPL-VW5000ES is alas a bit too much for the budget, so this may mean waiting for 3000lumen+ 4K projectors to become a bit more available.

Unfortunately insanity has set in. A very specific kind of insanity that I have seen several times before on AVS forum: rear projection light path optimisation insanity. First I considered extending the light path with precast concrete pipe segments, but that wasn't enough to get the incidence angle down. Then I realised that technically, no one can stop me from just digging a 2.8m wide x 1.2m high trench under the whole room and putting the projector down there. 9.5m throw distance means that I can use a 1.5 gain screen with only 20% centre to edge brightness variance; brightness up from 20 to 30 nits, which is still a bit low but maybe enough for rear projection.

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I've been considering a few screen layouts and an 8:3 aspect ratio with either 3 or 5 projectors looks ideal. One good quality 4K projector and some cheap 1080p projectors should suffice. 8:3 allows a 16:9 primary screen and two half-size 16:9 screens that can either be tiled (constant resolution) or showing separate content.

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Came up with a better idea for the walls/ceiling/floor that meets the non-theatre requirements and is not so horribly reflective. My new plan is to make a 6.7m x 6.7m metal cage out of 50mm pressed mild steel U channel (600mm spacing, welded joints). The 550mm x 550mm gaps in the cage can be infilled with perforated steel mesh, powdercoated black, 70% open for the walls and ceiling, 45% open for the floor. That can be backed by pyramidal sound absorber foam for the walls and ceiling; floor can be thick rubber underlay, with the 100mm ish intervening space holding the underfloor heating pipes (in air, no screed required). The open inner face of the U channels can be infilled with translucent perspex and LED backlit for the dimensional grid.

Sound absorbtion should be pretty good with a 70% open mesh backed by 100mm thick pyramid foam. I'll treat the main walls on the plenum behind as well with a thin foam. Everything except the perspex can be matt black. The whole cage can float off the floor as well, I'll put 10mm rubber bushings under the support points. Speakers will be hard mounted to the outer walls, not the inner cage. Would also act as a second layer Faraday cage inside the main (copper foil) Faraday cage as well. Now I just need to check the cost of welding approx 800 channel-to-channel T joints.

Ordered the screen : Stewart Filmscreen 100 rear projection material in the Luxus Deluxe frame, size 4.8m x 1.8m (201" diagonal, 8:3 aspect ratio). It will take a few weeks to make it across the atlantic. I'm now looking for practical and affordable first surface mirrors.

Quite the project....interested to see how it all turns out. I just finished (well this past summer) my conventional basement room theater. Was a lot of fun (well some of the stuff like drywall and tiling not so much) and I like seeing how different everyone goes about doing this stuff on their projects.

I'm just really keen to try rear projection. I've been front projecting for 20 years now, starting with an LCD tablet that fitted into an office-style overhead projector when I was a teenager; lots of friends have living room front projectors as well. Rear projection is something you only see at big commercial venues or concerts, but the advantages are compelling.

I've done rear projection mirror bounce rigs in professional environments. One mirror bounce isn't too complicated. When you get into two mirrors it is a lot more difficult to the he picture lined up and square. Commercial systems are designed so that you can actually put tension on the mirrors to warp (or unwarp) them to keep everything aligned. You really need a well designed rig with lots of adjustment or you will never get the image square.


If I am understanding correctly, you are planning on putting in a number of projectors in order to put multiple sources on the same screen. Any time you have overlapping projection images, it can be a hassle with regular projectors where you have short focal length lenses and you need to keeping each projector out of the projection cone of the others. Sometimes you get lucky with the available lenses, sometimes you don't. With a mirror bounce, it would be a nightmare. Your primary mirror will need to be huge and you will have a tough time keeping the mirror rigging and the projectors themselves our of the projection cones for the other projectors.


Hot spots with rear projection will always be a problem, but with multiple projectors, you will be complicating things greatly.


A much better way of doing this is to use a 4K projector and a commercial "multiviewer" that will allow you to fit multiple "picture in picture" type on one projection "canvas" in the different configurations that you want.

Well, the secondary 1080p projectors are kind of an experimental proposal, the primary projector is just a central 4K unit. However the geometry looks like it should work. The primary mirror is actually bigger than the screen, while the secondary mirror is the same width and only a little shorter (presumably tensioned mylar film on aluminium frames). The projection space is a 1.5m deep area behind the screen plus a huge tunnel under the floor. Support will be entirely from wall/ceiling/floor brackets with adjustement screws. So there should be plenty of freedom to position the projectors.

Took a long time to get the building regulations sorted out, but construction is now underway. Just completed the pile walls; went down to 12 metres with the 450mm R/C piles. Excavation of the main theatre/lab area starts next week. I did go with the optical trench under the floor design, despite significant cost to redesign the rebar; it's really the only practical way to get a rear-projected 200 inch screen. I've changed the floor/ceiling/walls to 'slate-effect' dark grey hard rubber tiles; hopefully the acoustics will be tolerable. Seating plan is still suspended, via 5 x 5 grid of 200kg rated hooks on the ceiling (just ordered some extra steel beams for this).

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How cool is this, and unique?

Have you priced the cost of front reflective mirrors?

It will certainly be unusual. Structural work should be done by end of June, interior might be done by Christmas if funding holds up.

Yes, the large 4.8m x 2.1m upper mirror will have to be a mylar tensioned frame type, the lower mirror is small enough to be a conventional first-surface rigid mirror.

The hole into which the HT will go;

I don't even know what to say about this. WOW

Anyone else think of Mike Mulligan and the Steam Shovel?

Unfortuantely there was a big delay in this project because the main contractor went bankrupt. I'm now self-managing and hiring in plant and labour as needed on day rates.

Poured the reinforced concrete rear projection trench; the projector will go in the thin part and the mirrors will go where the scaffolding tower is standing.





It's messy and hard work to shovel and tamp, but I prefer working with reinforced concrete to wood/drywall or masonry. It's extremely solid and sturdy once set, pretty much fireproof, lots of mass for dampening and you can make any shape you like quite easily. I'm planning to use galvanised corrugated steel roofing sheet for the interior formwork / wall covering (left in place), so the basement will be quite thoroughly Faraday caged.

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The foundation slab is in and work is progressing on the lower walls. The blockwork that's gone in so far is just formwork and retaining in case the walls collapse during construction, the load-bearing walls will be reinforced concrete. The projection trench is full of building materials at the moment; it will get a suspended floor over it during the screeding stage. The square holes in the walls are for the 500mm diam HVAC pipes (four cold air inlets and four warm air outlets). I will be spray-gluing acoustic foam into those tomorrow.



The project is using over 25 tonnes of steel, mostly rebar, and over 300 tonnes of concrete.



My son is doing his best to help out.



I've modified the floor plans to incorporate a wheelchair ramp, which will require some cantilevered pop-out alcoves on each side at the rear to get enough turning room to keep the gradient reasonable.

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I've been looking again at various options for floor/walls/celing, 6mm solid black rubber 'slate effect' tiles (for all three) seem like the best bet. I'll need a foam underlay as well, floor will be 50mm concrete screed over 100mm foiled insulation board, walls will be waterproofed drywall on steel studs (250mm cavity/plenum from the gavlanised steel structural wall; if I can find eggcrate foam with a low enough profile I'll treat inner and outer faces), ceiling will be suspended and infilled with rockwool. I've got the revised design from the structural engineer that increases the headroom to 9 feet before screeding, by using five smaller support beams instead of one huge one. Unfortunately this kind of stone-effect textured rubber only seems to come as tiles in 500mm & 1m sizes, not as a roll (like non-slip mat) or custom sizes. I've devised a scheme to cut down the 1m tiles to 600mm and reuse all the offcuts elsewhere in the building, but it's still pricy.

Slight issue with the LED strips in that I want the 60 chip per metre RGBW quad-chip strip for an even glow (not the 30 chip per metre or split colour/white chip stuff), but power consumption is 14W per metre. To make an 11 x 11 x 4 cuboid using 600mm tiles and LED diffuser strips in all the joints requires 400 metres of tape even allowing for the screen cutout, which is 5.6 KW of LED lighting. I could in principle fit that much driver capacity (I have three phase 415v power) and dim it down to something manageable (using amplifiers of course as no direct dimmer would take that wattage) but it would be crazy bright on full and a lot of wasted capacity for normal use. I'm thinking of instead using 4-channel chasing light controllers connected to the ground side of the strips, set to multi-KHz frequency so that there is no visible flicker. That would distribute the output of one driver/amplifier over 4 strips/segments equally, so effectively max brightness on the dimmer is only 20% brightness on each strip. Total power would be a more reasonable 1.4 KW which I could do with 3 x 500W drivers (one on each phase).

Formwork is in and work is underway on the lower walls. The formwork is galvanised steel corrugated panels with equal angle structural sections for the door frames and corners, all to be left in place (will add strength to the structure). The theatre area looks like it has two double door entrances, but those frames will contain sliding pocket door units, so it will actually be two single fire doors (3.5 feet wide each).



Main theatre/lab area will be 24 feet x 24 feet x 9 feet high before false walls or floor insulation/screed. Since this is a solid reinforced concrete structure two stories underground, detached from the house, sound isolation is not a concern other than lining the HVAC pipes with eggcrate foam. The false walls will be for air plenums and to hide speakers & wiring conduits.



This is the screen area with flat plywood formwork. You can see the four feet deep trench in the floor for the projector / rear projection throw distance; the alcove in the back wall will contain the two large first-surface polycarbonate mirrors.



I sometimes feel a kind of implied pressure to make this a standard theatre with recliners and riser and soffits and can lights and hush box and acoustic transparent front-projection, but I'm ignoring it. It's going to be something different.

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Love this ambitious project bitphase!!!

In the years ( ) that I have had planning my room (constructed very similarly to yours), I have gone back and forth between recliners and lower back couch-type seating. I know there are a couple options for low back recliners, but there are not enough IMHO...and the ones that are available are very expensive! Similar low-profile aspects of my build will be no front stage and slender surround speaker columns....will be employing can lights, AT screen, and some sort of method to hide the projector though.

Should be cool to see what you cook up!

I am concerned for your 24x24x9 dimensions...lots of ringing built into that geometry...but hoping you can mitigate it via acoustic treatments/processing.

Thanks, I'm the architect, project manager and surveyor so it is a lot of detail to keep track of. Some mistakes made and lessons learned but nothing too bad so far.

My plan is to build the ceiling with 25 x 1 tonne rated cargo hooks and get some of these : https://www.amazon.co.uk/Amazonas-AZ.../dp/B00GRYFB20 (they really are very comfortable) and/or these https://www.alfresia.co.uk/porto-ste...egg-chair.html paint them black (where necessary), install low power local LED lights, and hang them from the ceiling. Eight hanging seats would form the upper / main tier and I could bring in some low seats in front for large groups (or even bean bags for the kids).

If you're doing a from scratch build, have you considered rear projection? The modern screen materials don't show significant blur at a decent screen size and the ability to maintain high contrast ratio with house lights on is a trick no conventional design can match. The major issue is usually lack of projection space (or rather unwillingness to give up room size / seat count for projection space). In a custom build though you can bend it under the floor or ceiling, or just extend the building.

My plan is quarter inch solid rubber 'slate effect' (textured) jet black tiles on floor, ceiling and walls, backed by 1/2" drywall, mounted on steel studwork spaced 9" from the walls. I will put eggcrate sound insulation on the steel walls before the false walls go in and rubber strips under the studwork fixing U channels. The ceiling will be suspended 4" below the beams (which will be half-embedded in the slab), 12" below the bottom of the slab, with that cavity filled with rockwool. Since I don't need decoupling, just low frequency reflection dampening, thick rubber washers should suffice. Floor will be 4" solid foam insulation, 2" screed with heating pipes, quarter inch carpet underlay then quarter inch rubber tiles.

Square geometry is still not ideal for acoustics, but that is strongly preferable for some other uses of the room.

Memories of my childhood! My dad had a floating couch and coffee table suspended in the same manner in our living room for many years when I was a kid...the couch wasn't anything close to the assumed comfort of the ones in your links though.

I can honestly say the answer to that is 'no'. Haven't looked into it, but I'm guessing the 3-3.5' behind my baffle wall wouldn't accommodate it.

I recall reading one acoustician say "a square room is fixable; it will only require many more corrections (read: dollars and time) than a rectangular room"

Ah, you mean you've already built the room just not the theatre. Still, 3.5' is more than sufficient for a dual-bounce rear projection or even single bounce with a short throw lens. The reason that I've got such a long (25 foot) light path is that there is a compromise in chosing the rear projection screen material, between gain, lights-on contrast and uniformity. I've picked a material that maximises lights-on contrast and has decent gain (needed because the screen is 200" diagonal), but is sensitive to variations in incidence angle, i.e. if used with a short throw system there would be noticeable hot-spotting in the centre of the screen, while the corners would be darker. If you screen is smaller (e.g. 120, 140") or you can afford a 5000 lumen projector, you can use a lower gain material, shorter throw distance, and not get hot-spotting. Or alternatively you could use a lighter material that gives up a bit of lights-on contrast in return for viewing angle uniformity, but will be bright and still far outperform any front-projection system for lights-on use. This reduces the need for a separate room with a conventional TV for combined watching/playing/socialising.

Acoustic transparency is hard to combine with rear projection, greatly restricts your choice of materials if you insist. Personally though, I'm ok with just putting paired drivers above and below the screen. At reasonable seating distances (and head height matching the screen centre) the soundstage difference vs single central driver will not be noticeable by normal humans (hardcore audiophiles are a different subspecies I think).

Yep, the room is concrete walls right now. AT screen is a must for me though, so FP it is...guess I'm not as much of an outside-the-box thinker as I'd hoped...